The term Darwinian mechanism refers, of
course, to the menu of relevant natural processes
that are presumed by the vast majority of biologists to make biological
evolution and common descent possible. Here the key question is, In the
judgment of ID advocates, what are the relevant natural processes that belong
on this list? At minimum, the Darwinian mechanism menu includes genetic variation and natural selection. As
Dembskis expresses it, The Darwinian mechanism consists of random variation,
which provides the raw material for Darwinian evolution, and natural selection,
which sifts that material.

But there may be many more categories of
natural processes that have contributed to the success of biological evolution over
lifes formational history. Would ID proponents place all of these in the
category of Darwinian mechanism? Evidently not. For instance, in their
evaluation of the proposition that certain irreducibly complex biological
structures like bacterial flagella were formed by this mechanism, both Behe and
Dembski limit their evaluation to gradual
processes only, processes that bring about only minuscule functional
improvements (sometimes narrowly constrained to a single function) from
generation to generation. According to Behe, for instance, The key question is
this: How could complex biochemical systems be gradually produced?And in Behes book, Darwins Black Box,
the index listing for Darwinian evolution includes the parenthetical
clarification (gradualism).

In No Free Lunch,
Dembski tells us that The problem, then, is to coordinate the gradual
Darwinian evolution of an organism with the emergence of an irreducibly complex
system that the organism now houses but did not always possess.And what about various transformational processes or events that fall outside
of a strict gradualism? It seems that they are to be set aside as natural
processes that are not relevant to IDs evaluation of the Darwinian mechanism.
Ideas like coordinated macromutations, lateral gene transfer, set-aside cells,
and punctuated saltational events are thoroughly non-Darwinian.But the real question, it seems to me, is this: Whether or not these and other
such events are considered to fall within the bounds of a strict gradualist
definition of the Darwinian mechanism, are they relevant to the
formational history of life on earth? The historical development of novel biotic structures is no
respecter of the labels that we might choose to pin on the various factors
contributing to their actualization.

Another restriction on the menu of relevant natural processes considered by Dembski as
legitimate contributors to the Darwinian mechanism arises from his requirement
that scientific explanations regarding evolutionary processes must be causally specific. In Dembskis words, Causal specificity
means specifying a [natural] cause sufficient to account for the effect in
question.Lack of causal specificity leaves one without the means to judge whether a
transformation can or cannot be effected.

Full causal specificity is, of course, the
goal of all scientific explanations, but it is often very difficult to achieve,
especially in the reconstruction of lifes formational history. Thats just a
fact of life in evolutionary biology, as well as in many other areas of
science. What, then, should biology do? Abandon its search for natural causes?
Open the door to hypotheses regarding non-natural causation? Posit the
possibility of occasional form-conferring interventions by an unembodied
intelligent agent? Yes, says Dembski. In effect, that is the ID proposal. After
noting that science - when biased by naturalism - tends to restrict its search
for explanations to purely natural causes, Dembski argues: But in the absence
of causal specificity, there is no reason to let naturalism place such
restrictions on our scientific reasoning.

I suppose that one could grant the
possibility that this last point is technically correct, but one could equally
well argue that there are good
reasons - scientific, philosophical, and theological - why most of us do find positing the sufficiency of natural causes to be
warranted. Regardless of that, however, Dembski
introduces a serious problem into his analysis when he takes full causal
specificity to be a requirement for natural causes to be relevant contributions
to the Darwinian mechanism. Many scientific hypotheses regarding the manner in
which various transformational processes may have contributed to the
actualization of some new biotic structure might fall short of full
causal specificity - even though they may be highly plausible
applications of mechanisms that are at least partially understood. When that is
the case, the ID approach tends to denigrate them as nothing more than just-so
stories and to remove them from further consideration.If these scientific hypotheses do not exhibit sufficient causal specificity to
allow the computation of a numerical probability for success, then they are
likely to be dismissed from IDs consideration. Only those mechanisms that are
now fully understood, it seems, can be
placed on the menu of relevant natural processes contributing to the Darwinian
mechanism.

What is the net effect of this requirement
that only causally specific explanations count as relevant scientific accounts of how certain biotic
structures got actualized? I believe it throws the door wide open to false
positive claims regarding the need for non-natural explanations. No doubt there
are now numerous biotic structures for which science is unable to formulate
causally specific (detailed and complete) accounts of their actualization. In
the absence of full causal specificity (a quality, incidentally, that ID
demands of scientific explanations but not of its own explanations) the ID
movement does indeed have opportunity to posit its non-natural, intelligent
design explanations as logically permitted alternatives. However, each time a
new causally specific scientific explanation for one of these biotic structures
is developed, the ID explanation for its actualization immediately becomes
superfluous.IDs insistence that its claims can be refuted only by causally specific
scientific accounts stands as an open invitation to false positive claims
regarding the need for its appeal to non-natural causes.